Hyaluronic acid is a mucopolysaccharide that is abundantly present in various tissues (e.g., subcutaneous tissues, eyeballs, and joints) of a living body. Hyaluronic acid has been widely used as a cosmetic component due to a high moisturizing effect. For example, Japanese Patent No. 3221533 discloses a hair treatment agent that contains hyaluronic acid.
The surface of hair or skin is normally negatively charged. Hyaluronic acid is also normally negatively charged due to the presence of an anionic functional group (e.g., carboxyl group). Therefore, when treating hair using hyaluronic acid, hyaluronic acid and the hair repel each other since the surface of the hair and hyaluronic acid are negatively charged. Therefore, hyaluronic acid normally adheres to the surface of hair or skin to only a small extent. Accordingly, hyaluronic acid and a salt thereof that exhibit excellent adhesion to a living tissue (e.g., hair or skin) and exhibit a high moisturizing effect have been desired.